An often used means of selectively connecting a number of stations to respective transmission lines is through a crosspoint switching matrix. With this matrix, a station is connected to a selected transmission line by closing a specific crosspoint on the matrix. This closed crosspoint then serves to interconnect the station with the selected transmission line. To control the opening and closing of various crosspoints, a controller must be used.
Many types of controllers have been described which may be used in the crosspoint switching matrix of FIG. 1. With the advent of semiconductor crosspoint switches and the popularity of electronic switching systems, many of the recent controller designs have been implemented in integrated circuits, or a programmable computer has functioned as the controller. Examples of computerized switch controllers are given by Anderson in U. S. Pat. No. 4,331,956, by Bulfer in U.S. Pat. No. 3,935,394, and by McEowen et al in U.S. Pat. No. 4,196,316. However, almost all of these electronic switching networks have been designed for communication systems in which the switching can occur at a fairly leisurely pace because, once the interconnections have been established, the data lines remain connected to each other for substantial periods of time. However, in the case where the crosspoint switch is to be used within a computer or other computerized system and the interconnections are generally short-lived, a controller which requires a long time to establish the interconnections will severely reduce the effective bandwidth of the crosspoint switch. Alternatively stated, from the time a data line interconnection is requested until it is accomplished, no data can flow through the crosspoint switch, and accordingly, the throughput of the associated computer is reduced. Although a computerized controller will operate relatively fast, it requires a number of machine cycles to effect the connection after the service request has been made and suffers a corresponding delay. C. J. Georgiou describes in U.S. Pat. No. 4,630,045, application Ser. No. 544,653, filed Oct. 24, 1983, a controller for a crosspoint switch. A notice of allowance has been received for this application on May 27, 1986. Georgiou's controller is designed to be very fast, and only one controller is used. However, the controller must sequentially service multiple ports requesting connection through the crosspoint switching matrix. Once the demanded connection rate exceeds the speed of the controller, the throughput of the combined crosspoint switch and controller falls. Even if Georgiou's controller were redesigned to provide parallel subcontrollers, his parallel controller would nonetheless be dependent on a single table known as the port connection table. This table keeps track of available connections through the switch. Thus, the port connection table becomes a shared resource and limits the controller speed in case of high connection demand. U.S. Pat. No. 4,402,008 to K. Teraslinna describes an array of switches which are controlled by a latch which has a number of output leads connected to the switches of the array. Each output lead is connected to a particular switch of the array and is used to control the opening and closing of a particular switch.